If the symbol is defined, the call is included; otherwise, the call is omitted. Conditional methods provide a cleaner, more elegant alternative to enclosing the method call in #if conditionalSymbol...#endif preprocessor directives.(http://msdn.microsoft.com/en-us/library/4xssyw96%28v=vs.71%29.aspx) Using the Conditional attribute, you can isolate functions that should be part of your classes only when a particular environment variable is defined or set to a certain value.The Conditional attribute generates more efficient IL than #if /#endif does. It also has the advantage of being applicable only at the function level, which forces you to better structure your conditional code. (Effective C#:50 Specific Ways to Improve Your C# by Bill Wagner (Mar 15, 2010))

I saw many ppl have solution for add a watermaker to text fields. http://www.mkyong.com/jquery/jquery-watermark-effect-on-text-input/ http://www.davidjrush.com/blog/2011/10/jquery-creating-a-textbox-text-watermark/

But their solution is not what I want, because it set the value to the text field..and it will be submit with real data when you click submit button.

So I make some improvement.My solution is use a div to display watermaker message: